docs: def get_did_providers(self, did):
          """
          Return the list providers registered on-chain for the given did.
  
          :param did: hex str the id of an asset on-chain
          :return:
              list of addresses
              None if asset has no registerd providers
          """
          register_values = self.contract_concise.getDIDRegister(did)
          if register_values and len(register_values) == 5:
              return DIDRegisterValues(*register_values).providers
  
          return None